linux-kernel - Re: [PATCH v4 3/3] pwm: core: add consumer device link

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Date:   Tue, 19 Feb 2019 10:54:20 +0100
From:   Fabrice Gasnier <fabrice.gasnier@...com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
CC:     <thierry.reding@...il.com>, <robh+dt@...nel.org>,
        <tduszyns@...il.com>, <mark.rutland@....com>,
        <alexandre.torgue@...com>, <mcoquelin.stm32@...il.com>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-pwm@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH v4 3/3] pwm: core: add consumer device link

On 2/19/19 9:55 AM, Uwe Kleine-König wrote:
> On Tue, Feb 19, 2019 at 09:46:32AM +0100, Fabrice Gasnier wrote:
>> On 2/18/19 6:22 PM, Uwe Kleine-König wrote:
>>> Hello,
>>>
>>> On Thu, Feb 14, 2019 at 11:25:51AM +0100, Fabrice Gasnier wrote:
>>>> Add a device link between the PWM consumer and the PWM provider. This
>>>> enforces the PWM user to get suspended before the PWM provider. It
>>>> allows proper synchronization of suspend/resume sequences: the PWM user
>>>> is responsible for properly stopping PWM, before the provider gets
>>>> suspended: see [1]. Add the device link in:
>>>> - of_pwm_get()
>>>> - pwm_get()
>>>> - devm_*pwm_get() variants
>>>> as it requires a reference to the device for the PWM consumer.
>>>>
>>>> [1] https://lkml.org/lkml/2019/2/5/770
>>>>
>>>> Suggested-by: Thierry Reding <thierry.reding@...il.com>
>>>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
>>>> ---
>>>> Changes in v4:
>>>> - rework error handling following Thierry's comments
>>>> - turn/split pr_debug() into dev_err()/pr_warn().
>>>>
>>>> Changes in v3:
>>>> - add struct device to of_get_pwm() arguments to handle device link from
>>>>   there as discussed with Uwe.
>>>> ---
>>>>  drivers/pwm/core.c  | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
>>>>  include/linux/pwm.h |  6 ++++--
>>>>  2 files changed, 51 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
>>>> index 1581f6a..64e10a6 100644
>>>> --- a/drivers/pwm/core.c
>>>> +++ b/drivers/pwm/core.c
>>>> @@ -636,8 +636,35 @@ static struct pwm_chip *of_node_to_pwmchip(struct device_node *np)
>>>>  	return ERR_PTR(-EPROBE_DEFER);
>>>>  }
>>>>  
>>>> +static struct device_link *pwm_device_link_add(struct device *dev,
>>>> +					       struct pwm_device *pwm)
>>>> +{
>>>> +	struct device_link *dl;
>>>> +
>>>> +	if (!dev) {
>>>> +		/*
>>>> +		 * No device for the PWM consumer has been provided. It may
>>>> +		 * impact the PM sequence ordering: the PWM supplier may get
>>>> +		 * suspended before the consumer.
>>>> +		 */
>>>> +		pr_warn("no consumer dev, can't create device link to %s\n",
>>>> +			dev_name(pwm->chip->dev));
>>>
>>> Maybe use dev_warn(pwm->chip->dev, ...) ?
>>
>> Hi Uwe,
>>
>> I'm wondering a bit about this: In this case, the caller that doesn't
>> provide a struct device *, PWM provider isn't responsible for that. So I
>> just hope this wouldn't be miss-leading ?
> 
> IMHO it's more the wording that might make the message misleading. If
> you use
> 
> 	dev_warn(pwm->chip->dev, "No consumer device specified to create a device link to\n");
> 
> that's completely fine in my eyes.

Thanks for the suggestion, I'll update this as well in v5.

Best regards,
Fabrice
>  
> Best regards
> Uwe
>